The present invention relates to methods and compositions for use in subterranean operations. More particularly, the present invention relates to styrene-acrylate copolymers used to treat tar and/or crude oil resident in a well bore and associated methods of use.
Many subterranean operations involve the drilling of a well bore from the surface through rock and/or soil to penetrate a subterranean formation containing fluids that are desirable for production. In the course of drilling operations and other subterranean operations, the drillstring and/or other equipment may come into contact with zones of rock and/or soil containing tar and/or crude oil, such as heavy and light (liquid) hydrocarbons, asphalt, and bitumens; in man such operations, it may be desirable to drill the well bore through these zones containing tar and/or liquid crude. However, problems may be encountered when these zones are encountered. For example, crude oil present in the zone(s) may enter the well bore and emulsify or otherwise disperse into the drilling fluid. This is problematic in that contamination of the drilling fluid with the crude oil can undesirably impact the fluid properties, as welt as present complications with fluid disposal. If the drilling fluid is contaminated, extra precautions may need to be used for removal of the crude oil from the drilling fluid such that the surrounding environment is not polluted. Various techniques have been used to remove crude oil from drilling fluid to prevent oil pollution. In one technique, demulsifiers can be used to break the oil-in-water emulsion. In another technique, heat can be used to break the emulsion. However, both of these techniques can be difficult to implement in the field, as emulsification of crude oil into the drilling fluid can often form very strong emulsions that are hard to break.
In addition to problems drilling through liquid-crude-containing zones, problems may also be encountered when a zone or zones containing tar are encountered. Tar is a relatively tacky substance that may readily adhere to any surface that it contacts, including the surfaces of the well bore and/or any equipment utilized during the drilling operation. Tar also may dissolve into many synthetic treatment fluids used in the course of drilling operations, increasing the tacky and adhesive properties of the tar. If a sufficient amount of tar adheres to surfaces in the well bore or drilling equipment, it may, among other problems, prevent the drillstring from rotating, prevent fluid circulation, or otherwise impede the effectiveness of a drilling operation. In some cases, it may become necessary to remove and/or disassemble the drillstring in order to remove accretions of tar, a process which may create numerous cost and safety concerns. The accretion of tar on drilling equipment and/or in the well bore also can impede any subsequent operations downhole, including cementing, acidizing, fracturing, sand control, and remedial treatments. In addition, soft, tacky tar that manages to reach the surface may foul surface equipment, including solids screening equipment.
Existing methods of managing these problems that result from well bore tar incursion may be problematic. Some of these methods involve affecting an increase in hydrostatic pressure in the well bore so as to force the tar out of the well bore to the surface. However, this increased hydrostatic pressure may damage the well bore and/or a portion of the subterranean formation. Other conventional methods utilize treatment fluids that comprise dispersants, surfactants, and/or solubilizers, which allow the tar particles to dissolve in or homogenize with the treatment fluids. However, the tar particles may not be readily separated out of the fluid once they have dissolved into or homogenized with the fluid. The presence of the tar particles in the treatment fluid may alter its rheological properties and/or suspension capacity, which may limit its use in subsequent operations. Moreover, the addition of these dispersants, surfactants, and solubilizers may increase the complexity and cost of the drilling operation.